For example, in automotive manual transmissions, as shown in FIG. 27, it is conventional practice that a transmission gear 1 is supported rotatably via a radial roller bearing 3 that is assembled around the circumference of a power transmission shaft 2. In the radial roller bearing 3, a plurality of rollers 6 are provided so as to roll freely while being held by a cage 7 between a cylindrical outer ring raceway 4 provided on an inner circumferential surface of the transmission gear 1 and a cylindrical inner ring raceway 5 provided on an outer circumferential surface of the power transmission shaft 2. The inner ring raceway 5 may be provided directly on the outer circumferential surface of the power transmission shaft 2 or may be provided on an outer circumferential surface of a cylindrical inner ring that is provided separately. In the case of the construction shown in FIG. 27, the transmission gear 1 is positioned between a step portion 14 formed on the outer circumferential surface of the power transmission shaft 2 and a synchronizing hub 15 that is in spline engagement with the outer circumferential surface of the power transmission shaft 2.
Here, since the transmission gear 1 rotates in synchronization with the power transmission shaft 2, the radial roller bearing 3 is used in a state where the radial roller bearing 3 bears load and does not rotate relative to the transmission gear 1. However, with little load variation and long load bearing time, the rolling surfaces of the rollers 6 are kept in contact with the outer ring raceway 4 and the inner ring raceway 5 in the same position. Because of this, in the case of there being not much lubricant in the interior of the radial roller bearing 3, the oil film thickness at the contact portions becomes thin, resulting in fears that fretting corrosion is caused.
To prevent the generation of fretting corrosion as described above, it is conventional practice to apply a cage 7a (a so-called divided cage) shown in FIG. 28 to the cage 7 that is incorporated in the radial roller bearing 3 described above (refer to Patent Document 1). The cage 7a includes a pair of metallic cage elements 9 each having a partially cylindrical shape, and the cage 7a is formed into a cylindrical shape as a whole by aligning the pair of cage elements 9 in a circumferential direction. With the pair of cage elements 9 assembled together, the cage 7a includes a pair of arc-shaped rim portions 10 that are disposed coaxially in an axial direction (unless otherwise described, when used herein, axial and radial directions denote axial and radial directions of the cage. This will be true in the whole of the description and claims.) and a plurality of pillar portions 11 that are disposed at constant intervals in the circumferential direction in such a way as to connect together the pair of rim portions 10 in the axial direction. Outer circumferential surfaces of the pair of rim portions 10 and the plurality of pillar portions 11 reside on the same cylindrical surface along the full circumference.
Then, spaces surrounded by the pillar portions 11 that lie adjacent to each other in the circumferential direction and the pair of rim portions 10 make up pockets 12 for holding the rollers 6 in a rolling fashion. As shown in FIG. 27, an annular space 13 where the rollers 6 are disposed exists between the outer ring raceway 4 and the inner ring raceway 5. Total of circumferential lengths of the cage elements 9 are slightly shorter than a circumferential length of the annular space 13.
According to this construction, the cage element 9 that exists in a non-loaded range (an opposite side portion to a side power to which a radial load is exerted) of an annular space 13 is allowed to be displaced slightly in the circumferential direction. Owing to this, even in the event that the power transmission shaft 2 rotates in synchronism with the transmission gear 1, the contact portions between the rolling surfaces of the rollers 6 and the outer ring raceway 4 and the inner ring raceway 5 are allowed to move bit by bit, hence it is possible to prevent the generation of fretting corrosion at the contact portions.
Incidentally, the pair of cage elements 9 that make up the divided cage 7a described above do not have a function to refrain themselves from being displaced relative to each other in the axial direction. Then, the pair of cage elements 9 are restrained from being displaced relative to each other in the axial direction by a C-shaped snap ring 17 (a mating member) that is fitted in a recessed groove 16 that is provided on the power transmission shaft 2 via a flat washer 21. As shown in FIG. 29, the other axial end face 19 of the C-shaped snap ring 17 that is axially opposite to one axial end face of the radial roller bearing 3 (axial end faces 18 of the rim portions 10 of the cage elements 9) is formed into a discontinuous surface having a discontinuous portion 20 formed by cutting a circumferential portion of the other axial end face 19.